GREELEY, Colo. -- An Iraq War veteran who became an anti-war protester turned himself in after his ex-wife was shot and killed and her boyfriend seriously wounded in a violent and bloody confrontation.

Police said Ricardo Cortez went to a home on the 4400 block of West Sixth Street Sunday night and shot his ex-wife in the back and shot her boyfriend as he tried to flee.

Nikki Fix Cortez, 21, was killed by a shotgun blast and died in the kitchen.

Following a trail of blood and shell casings, police found Sam Jantz, 24, about three houses away. He had been shot several times as he ran for help. Witnesses said they could hear Jantz begging for help, pleading for his life.

"All I heard was someone saying, 'God help me,'"said Herb Wambolt, a neighbor.

"We heard a couple of big pops. And then I heard another round of shots followed by someone running and screaming, 'Oh my God! Oh my God, I've been shot. Somebody help me,'" said witness Hannah Montey.

Witnesses said that they could see that a man was chasing Jantz down the block, continually firing at him.

"The last boom-boom I heard was right here in my yard. I had already called 911 when the last shots were still going. So (the suspect) had to have unloaded eight to 10 rounds. It was just terrible," Montey said.

Jantz collapsed in Montey's yard and Montey, who heard it all, was frozen with fear.

"I'm 5 feet from my front door where I can't do anything but hide, for what I felt was for my safety. And I will probably have guilt for the rest of my life -- feeling like I couldn't save somebody begging for their life," Montey said.

Rich Strang, a former police officer, heard the man screaming for help and jumped into action.

"His reaction was to grab his gun and go find out what was going on. He kept hearing, 'Help me, help me.' So he went to the guy saying 'help me' and was there," said Tamara Strang, Rich's wife.

Jantz was listed in critical condition at North Colorado Medical Center.

Police arrested Ricardo Cortez, 24, after he turned himself in to police Monday morning. He was accompanied by his parents. Cortez was arrested on suspicion of first-degree murder, attempted first-degree murder, first-degree burglary and violation of a restraining order.

The restraining order originated from a domestic violence case that occurred in March when Ricardo Cortez was accused of assaulting Nikki Cortez and holding her against her will.

Police went to the home of Ricardo Cortez's parents and found his car, a 1998 Ford Contour, parked in front of the house. A deputy spotted a shotgun lying in the back seat and called for the vehicle to be impounded.

Investigators must wait for forensic tests to determine if the shotgun that was found is the murder weapon. They were conducting additional searches as part of their investigation.

The Greeley Tribune has a picture of Ricardo Cortez from an anti-war protest that he had organized in March, where he identified himself as a Navy medic who was in Iraq in 2003 and in 2004.

Nikki Cortez and Jantz had just returned from a date when they were killed. Jantz lives with his sister and her husband, Sara and Alan Karnitz. The Karnitzes told police that while Nikki and Sam were away, Ricardo Cortez stopped by the home asking to see Nikki. When Nikki and Jantz returned and were told what happened, Nikki started apologizing for her estranged husband.

That's when Ricardo Cortez came into the house uninvited, carrying a shotgun, Alan Karnitz said. Karnitz and his wife ran to the bedroom and said they could hear gunshots and Nikki screaming for help.

Ricardo Cortez and Nikki were in the middle a divorce, authorities said.

Cortez is being held without bond. He is expected back in court Sept. 19.